The present invention relates to a method and apparatus for determining the location of defects, such as cracks in various products, such as multiplayer laminates for small aircraft, boats and the like; and more particularly, relates to a method and apparatus for determining the thickness of a sample and defect depth using thermal imaging in a variety of plastic, ceramic, metal and other products.
Determining defect depth with thermal imaging or thermography has received extensive study from researchers in academia and industry for many years. Traditional thermograph techniques have involved manual examination of acquired thermal images to identify defects. The operator must proceed through a series of thermal images taken within a specific time period to look for hot spots and assess their contrast against the surroundings in order to estimate their relative depths. This process is very time consuming and provides only qualitative data.
Non-destructive testing using transient thermography which relies upon the transfer of heat through an object over a period of time is known in the art. For example, U.S. Pat. No. 5,711,603, issued Jan. 27, 1998 to Ringermacher et al. and entitled xe2x80x9cNONDESTRUCTIVE TESTING:TRANSIENT DEPTH THERMOGRAPHYxe2x80x9d discloses a non-destructive testing technique and system using transient depth thermography. The disclosed method requires the construction of a reference temperature/time curve from the average temperatures of the entire images. As a result, sample heating must be uniform during the experiment, which is difficult to achieve in large samples, and the sample must have a uniform thickness. The disclosed method uses a six point average scheme to calculate the derivative of temperature contrast in order to suppress the high signal noise due to data subtraction and differentiation operations. This smoothing scheme may significantly reduce the accuracy of the predicted depth. Predicted depth is expressed as a relative depth to the sample thickness and is not an absolute value of depth. These problems make the disclosed method less accurate and less useful for general applications.
A principal object of the present invention is to provide a method and apparatus for determining the thickness of a sample and defect depth using thermal imaging in a variety of plastic, ceramic, metal and other products.
It is another object of the invention to provide such thermal imaging method and apparatus for determining the thickness of a sample and defect depth that accurately provides defect depth.
It is another object of the invention to provide such thermal imaging method and apparatus for determining the thickness of a sample and defect depth that allows for testing a variety of surfaces.
It is another object of the invention to provide such thermal imaging method and apparatus for determining the thickness of a sample and defect depth that preferably uses one-sided thermal imaging where the source of heat energy and an infrared camera or other sensing equipment are on the same side of the sample.
It is another object of the invention to provide such thermal imaging method and apparatus for determining the thickness of a sample and defect depth substantially without negative effect and that overcome many of the disadvantages of prior arrangements.
In brief, a method and apparatus are provided for determining the thickness of a sample and defect depth using thermal imaging in a variety of plastic, ceramic, metal and other products. A pair of flash lamps is positioned at a first side of the sample. An infrared camera is positioned near the first side of the sample. A data acquisition and processing computer is coupled to the flash lamps for triggering the flash lamps. The data acquisition and processing computer is coupled to the infrared camera for acquiring and processing thermal image data. The thermal image data are processed using a theoretical solution to analyze the thermal image data to determine the thickness of a sample and defect depth.